1. Field of the Invention
The present invention relates to an electroless plating apparatus and method which are preferably used for forming interconnects on a semiconductor substrate (including filling of a metal such as copper into an interconnection groove or the like, forming of a seed layer, and forming of a reinforcing seed layer on a seed layer for the purpose of reinforcing the seed layer), an interconnection-protective film, and a diffusion-preventive film.
2. Description of the Related Art
An electroless plating is such a method that a plated film is formed on a surface of a material to be plated by chemically reducing metal ions in a plating liquid without supplying any electric current from the outside, and electroless plating is widely used in nickel-phosphorus plating and nickel-boron plating for providing corrosion resistance and wear resistance, and copper plating for a printed-wiring substrate.
As an electroless plating apparatus, there has been generally known an apparatus comprising a plating bath for holding an electroless plating liquid while causing the electroless plating liquid to overflow, and a vertically movable holding portion disposed above the plating bath for holding a material, to be plated, such as a substrate so as to face laterally, whereby the material, to be plated, held by the holding portion is dipped into the plating liquid in the plating bath (the so-called dipping(dip)). Further, there has been also generally known an apparatus comprising a holding portion for holding a material, to be plated, such as a substrate so as to face upwardly (face up), and a plating liquid supply portion for supplying a plating liquid to an upper surface (surface to be plate) of the material, to be plated, held by the holding portion, whereby the plating liquid flows along the upper surface of the material, to be plated, held by the holding portion. As a face-up type plating apparatus, there is a coater face-up type plating apparatus in which a plating liquid flows along an upper surface of a material to be plated by supplying the plating liquid to the upper surface of the material to be plated from the plating liquid supply portion and rotating the material to be plated.
In recent years, as the processing speed and integration of a semiconductor chip becomes higher, there has been a growing tendency to replace aluminum or aluminum alloy with copper having a low electric conductivity and a high electromigration resistance as metallic materials for forming interconnection circuits on the semiconductor substrate. This kind of copper interconnect is generally formed by filling copper into fine recesses formed in the surface of the substrate. As a method for forming the copper interconnect, plating is generally used. In any case, after a copper film is deposited on the surface of the substrate, the surface of the substrate is polished to a flat finish by chemical mechanical polishing (CMP).
An electroless plating is applied to main filling materials (Cu) for the copper interconnect, the formation of the seed layer on the barrier metal, or the reinforcement of the seed (Cu), further the formation of the barrier metal itself, or the formation of cap material for the copper interconnect (in any case, Nixe2x80x94P, Nixe2x80x94B, Coxe2x80x94P, Nixe2x80x94Wxe2x80x94P, Nixe2x80x94Coxe2x80x94P, Coxe2x80x94Wxe2x80x94P), or the like. In any electroless plating process, uniformity of the film thickness over an entire surface of the substrate is required.
In this case, in the electroless plating, as soon as a material to be plated is brought into contact with a plating liquid, a plating metal begins to be deposited on the surface to be plated, and the deposition velocity of the plating metal varies with the temperature of the plating liquid. Thus, in order to form a plated film having a uniform thickness on the surface of the material to be plated, it is necessary that the temperature of the plating liquid should be uniform on the entire surface to be plated from the time when the plating liquid begins to be brought into contact with the material to be plated, and should be kept constant during all the plating process of this contact, and the velocity distribution (thickness of a diffusion layer or a boundary layer formed along the surface to be plated) of the plating liquid in a direction perpendicular to the surface to be plated during the plating process should be uniform over the entire surface to be plated.
However, in the conventional dip type and jig fixing type plating, it has been difficult to make a flow of the plating liquid on the substrate uniform. Further, in the coater face-up type plating, there has been problems of a control of flow and a uniformity of liquid temperature.
FIG. 11 is a schematic view showing a conventional dip type electroless plating apparatus. As shown in FIG. 11, this electroless plating apparatus comprises a plating bath 280 for storing a plating liquid 281 therein, and a substrate holding apparatus (substrate holding means) 290 for holding a semiconductor substrate W.
In the electroless plating, a good reaction cannot take place unless the temperature at the contacting portion between a surface W1, to be plated, of a semiconductor substrate W and a plating liquid is kept at a predetermined temperature (for example, 60xc2x0 C.). Therefore, in order to heat the plating liquid 281 in the plating bath 280 and keep the plating liquid 281 at a predetermined constant temperature, a pipe 282 is connected to the plating bath 280 to withdraw the plating liquid in the plating bath 280 and to circulate the plating liquid by a pump P, and there is provided a heating apparatus (heating means) 283, in the pipe 282, such as a heater for heating the plating liquid to a predetermined temperature.
On the other hand, the substrate holding apparatus 290 is formed into such a shape that the substrate holding apparatus 290 covers the surface of the semiconductor substrate except for the surface W1, to be plated, of the semiconductor substrate W, and is adapted to dip the semiconductor substrate W into the plating bath 280 in such a state the surface W1 to be plated is placed in a vertical direction. The reason for placing the surface W1, to be plated, of the semiconductor W in a vertical direction in the plating bath 280 is that gas is generated on the surface W1 to be plated by a plating reaction, and if the generated gas remains on a certain area of the surface W1 to be plated, the plating reaction is obstructed at such area, and hence such generated gas is required to be easily separated from the surface W1 to be plated.
However, in the above conventional electroless plating apparatus, because the surface W1, to be plated, of the semiconductor substrate W must be placed vertically in the plating bath 280, the plating bath 280 is required to have a large depth, and thus cannot be downsized. Further, because it is necessary to provide the heating apparatus 283 outside the plating bath 280, an overall apparatus cannot be downsized also in this respect.
On the other hand, in the case where a copper plating is applied to the semiconductor substrate W, when the temperature of the plating liquid varies by 1xc2x0 C. in a plating time of one minute at, for example, around 60xc2x0 C., the difference of the film thickness amounts to approximately 1.8 nm, and hence an extremely precise temperature control of the plating liquid is required. However, as described above, the plating bath 280 cannot be downsized, and thus a large amount of the plating liquid is required to be contained. Consequently, the temperature of the plating liquid cannot be precisely controlled, and the amount of the plating liquid to be used increases to thus increase electric power consumption for heating the plating liquid and keeping the plating liquid warm.
The present invention has been made in view of the above drawbacks. It is therefore a first object of the present invention to provide an electroless plating apparatus which can easily form a plated film having more uniform thickness on a surface, to be plate, of a material to be plated.
A second object of the present invention is to provide electroless plating apparatus and method in which an overall apparatus can be downsized, the amount of a plating liquid to be used can be small, and the temperature of the plating liquid can be precisely controlled.
In order to achieve the first object, according to a first aspect of the present invention, there is provided an electroless plating apparatus comprising; a holding portion having a heating portion for holding a material to be plated in such a state that a surface to be plated faces downward; and a plating bath for introducing an electroless plating liquid having a predetermined temperature into a plating chamber, and holding the electroless plating liquid while allowing the electroless plating liquid to overflow an overflow dam; wherein the material, to be plated, held by the holding portion is brought into contact with the plating liquid in the plating bath to plate the material. The electroless plating liquid is preferably introduced into the plating bath by an upward flow.
In this case, the heating portion may be attached to the holding portion or may be integrally provided in the holding portion. The built-in heating portion is preferable because heat can be effectively and uniformly transferred.
With this arrangement, while holding the material, to be plated, by the holding portion and heating the material, to be plated, to the same temperature as that of the plating liquid by the heating portion provided in the holding portion, the material to be plated is dipped in the plating liquid having a predetermined temperature to perform a plating treatment, thereby preventing the surface of the material, to be plated, from becoming nonuniform temperature distribution and preventing the plating temperature from being changed during a plating process. Further, by creating a stable flow of the plating liquid flowing upwardly and spreading outwardly in the plating chamber, the velocity distribution (thickness of a diffusion layer or a boundary layer) of the plating liquid in a direction perpendicular to the surface of the material to be plated can be more uniform over an entire area of the surface to be plated during the plating process.
The temperature of the plating liquid to be introduced into the plating bath is in the range of, for example, 25 to 90xc2x0 C., preferably 55 to about 80xc2x0 C., and the flow rate of the plating liquid is in the range of, for example, 1 to 30 l (liter)/min, preferably 1 to 20 l/min, and more preferably 1 to about 10 l/min. However, the optimal flow rate of the plating liquid varies with process temperature and reducing reaction state.
According to a preferable aspect of the present invention, the holding portion is adapted to be freely rotatable. With this arrangement, by holding and rotating the material to be plated by the holding portion, the velocity distribution of the plating liquid in a direction perpendicular to the surface, to be plated, of the material during a plating process can be more uniform. This rotational speed is in the range of, for example, 0 to 100 rpm (0 to 100 minxe2x88x921), preferably 0 to about 50 rpm (0 to 50 minxe2x88x921). However, these optimal rotational speeds vary with reducing reaction state and required uniformity of the film thickness on the surface.
According to a preferable aspect of the present invention, at least an area of a bottom surface of the plating chamber which faces the material, to be plated, held by the holding portion has a quadratic curved surface spreading upwardly and outwardly.
With this arrangement, in the area having a quadratic curve on the bottom surface of the plating chamber, the plating liquid flows smoothly in a laminar flow along the bottom surface of the plating chamber without generating vortex locally while flowing.
According to a preferable aspect of the present invention, a heating portion for heating the plating liquid held by the plating bath or a heat insulating material for heat insulation of the plating liquid from the outside is provided in the plating bath. Thus, the plating liquid having, for example, a high temperature can be prevented from being gradually cooled while flowing in the plating bath.
According to a preferable aspect of the present invention, the holding portion is adapted to hold the substrate by a vacuum chuck or an electrostatic chuck.
In the case where a uniform flow of the plating liquid on the substrate is considered to be formed, the seal located at the outer peripheral portion of the substrate becomes a factor to disturb the flow of the plating liquid. In order to further improve accuracy of uniformity of the surface, it is desirable that there is no seal on the surface, to be plated, of the substrate. Thus, the chuck should hold the backside of the substrate, the vacuum chuck or the electrostatic chuck should be used, and the seal should be performed at the outer periphery of the backside of the substrate.
According to an aspect of a substrate processing apparatus of the present invention, the substrate processing apparatus comprises the electroless plating apparatus for forming a plated film on a surface of the substrate, and an apparatus for forming a catalyst layer before applying electroless plating to the surface of the substrate by the electroless plating apparatus.
In order to achieve the above second object, according to a second aspect of the present invention, there is provided an electroless plating method comprising: facing a surface, to be plated, of a substrate downwardly; and processing the surface to be plated by bringing the surface to be plated into contact with an electroless plating treatment liquid.
With this arrangement, the surface to be plated can be easily brought into contact with the plating treatment liquid. Further, the amount of the plating treatment liquid to be used can be reduced and the temperature of the plating liquid can be accurately and easily controlled, and the electric power consumption for heating the plating treatment liquid and keeping the plating treatment liquid warm can be decreased.
In this case, by bringing the surface to be plated into contact with the electroless plating treatment liquid in such a state that the surface to be plated is inclined, gas generated on the surface to be plated can be effectively removed from the surface to be plated.
Further, gas generated on the surface to be plated is removed from the surface to be plated by forming a flow of the electroless plating treatment liquid in a certain direction on the surface to be plated and entraining the gas generated on the surface to be plated with the flow of the electroless plating liquid.
According to a second aspect of the present invention, there is provided an electroless plating apparatus, comprising: a plating treatment liquid holding apparatus for storing a plating treatment liquid while maintaining the plating treatment liquid at a predetermined plating treatment temperature; and a substrate holding apparatus for holding a substrate in such a state that a surface, to be plated, of the substrate faces downwardly, and bringing the surface, to be plated, of the substrate into contact with the plating treatment liquid.
With this arrangement, the plating treatment liquid holding apparatus can be downsized, and an overall apparatus can be downsized.
The plating treatment liquid holding apparatus preferably has a heater at a bottom surface of the plating treatment liquid holding apparatus, and a dam for holding the plating treatment liquid over a periphery of the heater.